The invention relates to foot pedal devices for controlling engines without the need for a direct mechanical connection between the pedals and the engines. The invention is particularly directed to providing a drive-by-wire system, i.e., driving by electrical or electronic means, rather than by mechanical links.
In the prior art, accelerator pedals are used to mechanically control a vehicle engine and usually include a pedal mounted to a vehicle body with a series of links and levers, or Bowden cables, connecting the pedal to the carburetor, fuel injector, controller, or other similar device. These linkages must be designed to withstand and accommodate engine movements relative to the vehicle frame, as well as to provide accurate control despite such movements. In addition, packaging space must be provided for the linkages to function properly. The space available for routing the mechanical control links, rods, and cables is limited. When electrical sensors are used to monitor the position of the pedal, connection to the carburetor or other engine device can be accomplished with electrical wiring, which is more easily routed through the vehicle.
In drive-by-wire applications, it is important that the pedal system provide the customary feel and performance of a mechanical linkage. The pedals must function responsively to driver input and must provide non-fatiguing resistance. Drivers are accustomed to applying and releasing pressure on a pedal arrangement and become accustomed to the resistance to application of force to the pedal as well as to the rate of withdrawal as the applied pressure is relaxed. With the present invention, the customary feel during the application of force to increase speed and while maintaining speed, as well as the familiar deceleration movement of the pedal can be duplicated in a wire type control.
The accelerator pedal is connected to a potentiometer or other sensor that is used to monitor the position of the pedal with respect to a reference point. The potentiometer generates a signal that varies in magnitude with respect to the pivotal position of the accelerator pedal. This signal is sent to a computer processor that is wired to the potentiometer. The processor uses the sensor signal along with various other parameters to generate a control signal for controlling the position of the engine throttle through a wire connection.
The accelerator pedal is operable between an idle position and a maximum travel position. When a force is applied to the pedal, the pedal pivots to an operating position somewhere between the idle and maximum travel positions. Sometimes the driver will desire a fast acceleration, which will cause the automatic transmission to change to a next lower gear. In a mechanical linkage, when the transmission makes this downshift, a certain feel is imparted to the driver's foot via the pedal assembly. This feel is referred to as kickdown. An example of a kickdown mechanism that is used to initiate a transmission downshift for a pedal that is mechanically linked to an engine throttle is shown in U.S. Pat. No. 5,697,253. With the present invention, the customary feel during the downshift can be duplicated in a wire type control such that the driver can feel the kickdown at the pedal.
An example of an electrical kickdown switch used in an electronic throttle control pedal assembly to initiate a transmission downshift is shown in U.S. Pat. No. 5,806,376. However, these electronic control pedal assemblies do not include a mechanical mechanism for imparting the kickdown feel to a driver. The present invention provides an electronic throttle control pedal assembly with a kickdown generating mechanism that imparts a transmission shift feel to the driver. The kickdown generating mechanism requires few components, is easy to maintain, and is easily assembled into an electronic throttle control pedal.